Furfural extraction of middle distillates



United States Patent 3,539,504 FURFURAL EXTRACTION 0F MIDDLE DISTILLATESBilly H. Cummins, Nederland, Tex., assignor to Texaco Inc., New York,N.Y., a corporation of Delaware No Drawing. Filed Dec. 12, 1968, Ser.No. 783,422 Int. Cl. Cg 21/16 US. Cl. 208327 11 Claims ABSTRACT OF THEDISCLOSURE A process for preparing middle distillate fuels with improvedburning qualities and color utilizing a furfural solvent extractionprocess wherein the solvent during the process contains color impuritiesby contacting a middle distillate charge stock with a furfural solventat an upper raflinate temperature above about 150 F. separating aprimary raffinate phase from a primary extract phase, reducing thetemperature of the primary raffinate phase to Within the temperaturerange of from about 60 F. to about 130 F. and maintaining thetemperature of the secondary extract and secondary raflinate phasesduring separation of the phases within such temperature range.

This invention relates to a solvent extraction process for producingmiddle distillate fuels with improved burning qualities and color andmore particularly to a process utilizing a furfural solvent whichcontains color impurities.

Generally speaking, solvent extraction operations are well known in theart. Ordinarily, in one form of operation, a liquid-liquid extraction isaccomplished by feeding a material to be extracted, that is, a chargestock in which there are present at least two different chemicalentities which have different solubilities or preferences in thepresence of each other or a solvent, into a solvent extraction zone inwhich the charge stock is contacted with a solvent, usually incountercurrent flow. At one end of the zone, there is removed arafiinate portion which represents that chemical entity which is not assoluble in the solvent and at the other end an extract phase whichcontains said other entity.

Prior art solvent extraction processes in general require temperaturesof operation usually in the range of from 200 F. to 250 F. In certainsolvent extraction process a temperature differential between the bottomand top portion of the extraction zone is utilized, that is a bottomextract temperature of from about 150 to 160 F. and an upper rafi'inatetemperature of from ZOO-250 F.

A problem associated with the manufacture of middle distillate fuels andparticularly kerosene is the requirement that such fuels have good colorand burning qualities. In order to improve the good burningcharacteristics of, for example, a kerosene fuel, it is necessary toutilize various refining processes such as extraction, distillation andadsorption techniques to remove aromatics and olefins. A particularproblem that is encountered during processes to improve burningcharacteristics of a kerosene type is that color bodies can be impartedto the kerosene which can completely alter the color characteristics ofthe fuel. It therefore is important in the refining of kerosene fuels toproduce not only kerosene having good burning characteristics but alsoacceptable color.

During the solvent extraction processes utilizing furfural as a solventa problem is encountered during the extrac tion process of colorrejection to the raflinate phase. It has been found that during thefurfural solvent extraction of a middle distillate fuel utilizingfurfural as a solvent a color develops in the furfural phases, possiblydue to the polymerization or oxidation of the furfural (e.g., a

3,539,504 Patented Nov. 10, 1970 color impurity), which is imparted tothe raflinate (fuel) phase and subsequently to the fuel phase.

It is therefore an object of this invention to prepare a middledistillate fuel having good burning characteristics and good colorutilizing a furfural extraction process wherein the furfural solventcontains color impurities.

It has now been found that a middle distillate fuel can be producedhaving good burning characteristics and color utilizing a furfuralsolvent extraction process wherein the furfural solvent during theextraction process contains color impurities by contacting a middledistillate charge stock with furfural solvent in an amount sufficient toform a primary extract and a primary raflinate phase wherein theraflinate outlet temperature is maintained above about 150 F.,separating a primary raffinate phase from the primary extract phase,reducing the temperature of the primary rafiinate phase to below about135 F. and maintaining the temperature of the secondary extract andsecondary rafiinate phase, during separation of the phases below about135 F., generally Within a temperature range of from about 60 F. toabout 130 F. In carrying out the process of this invention a middledistillate charge stock (hereinafter referred to as charge stock) ischarged into a separator together with furfural solvent, the amount offurfural solvent being sufficient to form a primary extract and aprimary raffinate phase and a raffinate outlet temperature is maintainedabove about 150 F. The primary raflinate phase is then separated fromthe primary extract phase and the temperature of the primary rafiinatephase is reduced to below about 135 P. such that a secondary extract andsecondary ratlinate phase are formed. A temperature below about 135 F.generally Within the range of from about 60 F. to about 130 F. is thenmaintained during separation and recovery of at least about a majoramount of the secondary raflinate phase from the secondary extractphase. A middle distillate fuel is then recovered from the secondaryrafiinate phase. The criterion of this invention is that the temperaturebe maintained below about 135 F. preferably Within the range of fromabout 60 F. to about 130 F. By the use of the term maintaining atemperature is meant that this temperature has to be maintained onlyduring that time when color can be imparted to or remains in thesecondary rafiinate phase. Thus a temperature within the above range ismaintained during separation of the two phases and such temperature isgenerally an average temperature during such separation of the secondaryextract and raffinate phases. It has been found that if separation ofthe two phases takes place below about 135 F. or Within this temperaturerange a middle distillate fuel is obtained which has improved colorwhereas the middle distillate fuel recovered from the primary rafiinatephase is considerably darker than the middle distillate charge stock.The preferred temperature range is from about F. to about 130 F. andstill more preferably within the range of from about F. to about F.

A particularly preferred embodiment of this invention comprises theprocess of charging a middle distillate charge stock together withfurfural solvent in countercurrent flow to a separator at a toprafiinate temperature above F. such as a top raflinate temperature inthe range of from about F. to about 240 F. to form a primary extract andrafiinate phase and separating the primary raffinate phase from theprimary extract phase. The primary rafiinate phase is then reduced intemperature to Within the range of from about 60 F. to about 130 F.wherein a secondary raflinate and secondary extract is formed. Thesecondary rafiinate is separated from the secondary extract and a middledistillate fuel is obtained which has improved color and burningcharacteristics as compared to the feed obtained from the originalprimary raflinate utilizing higher extraction temperatures.

The middle distillate charge stock, in general, can be naphthas,kerosenes, gas oils, catalytic cycle gas oils, and similar boilingvirgin distillates.

The ratio of solvent to charge stock in liquid-liquid extractions, mustbe suflicient to exceed the solvent solubility under the extractionconditions in said charge stock in order to form two distinct liquidphases, viz, a primary raffinate phase containing little or no solventand an immiscible primary extract phase comprising the solvent andextracted hydrocarbons. Generally, from about 0.5 to about volumes ofsolvent per volume of middle distillate charging stock is utilized.Ordinarily from about 1 to about 5 volumes of solvent per volume ofcharge stock is utilized, especially in the treatment of keroseneboiling range stocks (about 500 F. end-point). Sufiicient pressure ismaintained within the extraction zone to prevent substantialvolatilization of the charge stock or solvent under the liquid-liquidextraction conditions. Usually pressures within the range of about 0 toabout 100 p.s.i. are suflicient, it being appreciated that theparticular pressure which is required in a given case can readily bedetermined by experiment.

Any means of separating extracted materials from the extract phase andof recovering solvent therefrom may be employed. Thus under certainconditions, it may be desirable to distill extracted materials from theextract phase or to wash them out of the extract layer with a paraffinhydrocarbon having a different boiling point. Also, the solvent may insome instances be recovered from the extract phase by crystallization orby washing with a solvent which is highly selective therefore, such asethers, etc.

The raflinate phase (or in extractive distillation, the distillate) canbe treated by conventional methods to effect further refining thereofsuch as distillation. Thus, the rafiinate or distillate can be washedwith water, aqueous alkalies, etc., treated with adsorbent solids suchas activated carbon, activated clays, etc., redistilled, or acombination of the above processes. In addition the furfural from thesecondary rafiinate and the primary and secondary extract phases can berecycled to the extraction zone for use as a solvent. In addition in thecase of the preferred process, the secondary extract can be recycled tothe primary extraction zone at a point preferably below the introductionof the furfural and above the introduction of the charge stock.

In carrying out the process of this invention, furfural solvent isintroduced into an extraction zone in countercurrent flow with thecharge stock. By the use of the term furfural solvent is meant thatfurfural is used as the primary solvent. Thus auxiliary solvents andanti-solvents can be utilized in combination with furfural. In general,it is preferred to use a major amount of furfural in the furfuralsolvent system more preferably 80 percent by weight furfural and stillmore preferably 90 percent by weight furfural. In a preferred embodimentof this invention the furfural solvent system is substantially furfuralthat is over 90 percent by weight furfural. It may be desirable toemploy diluents or auxiliary solvents (including anti-solvents) inspecific cases in order to modify selectivity of the furfural solvent,to lower the melting point of the furfural solvent to permit its use atlow temperatures, or for other reasons. The amount of auxiliary solventcan be selected with reference to specific cases; generally up to aboutweight percent or more, based on the furfural solvent, can be employed.The auxiliary solvent should be miscible to the desired extent with thefurfural solvent, and should preferably be a neutral compound. Asexamples of auxiliary solvents which can be employed are water, thesulfolanes, for example, 2,4-dimethylsulfolane, 2,3-dimethylsulfolaneand the like; various nitriles such as acetonitrile, bis-Z-cyanoethylether and the like; various ethers such as diethyl ether,methyl-tertbutyl ethers; glycols or their ethers, tetrahydrofuran andthe like; halogenated hydrocarbon solvents such as chloroform, carbontetrachloride, ethylene dichloride, trichloroethane, tetrachloroethaneand the like; esters of carbonic acid, monocarboxylic acids, anddicarboxylic acids, for instance, diethyl carbonate, bis-Z-hydroxyethylcarbonate, bis-Z-chloroethyl carbonate, bis-2-methoxyethyl carbonate,ethylene carbonate, n-butyl formate, methyl furoate, dimethyl oxalate,diethyl succinate, dimethyl phthalate, dimethylisophthalate, and thelike; neutral organic nitrogen compounds such as N,N-dialkyl formamides(particularly dimethyl formamide), nitro aromatics such as nitrobenzeneand the like; kctones, for example, methyl ethyl ketone, methyl isobutylketone and the like, crotonaldehyde and the like; butylrolactone,butylrolactam, etc.

Anti-solvents or diluents may also be employed in the practice of thepresent invention. Thus, diluents such as saturated hydrocarbons,perfluorocarbons, perfluoroamines, perfiuoroethers, etc., may be addedto the charge stock or introduced directly into the extraction zone.

In the extraction, a small proportion of a suitable surface-active agentmay be added to increase the efiiciency of extraction equipment. Thus,long chain esters of perfluoroalkyl alcohols or perfluoroalkyl acids,perfluoroalkyl amides and amines, etc., may be employed, in suitableconcentrations between about 0.0001 and about 1 weight percent, based onthe weight of the solvent (note G. B. Blake et al.-paper presentedbefore the Division of Petroleum Chemistry of the American ChemicalSociety, September 1954 p. 313 if).

The present invention can be carried out in batch, con tinuous orsemi-continuous operating cycles, and in one or more actual ortheoretical stages, employing contacting and separation equipment suchas has heretofore been employed in the selective solvent refining ofpetroleum stocks. In addition a multi-stage mode of operation that is arepeating of the process several times can be utilized in carrying outthe process of this invention. Various types of liquid-liquid extractionoperations and suitable extraction equipment are described, for example,in Chemical Engineers Handbook (McGraw-Hill Pub lishing Co., Inc., N.Y.,1950), pp. 716 ff. and 474 if. It should be understood that the specificequipment employed forms no part of the present invention and that anyequipment adaptable for the purposes of contacting the furfural solventwith the charge stock and thereafter separating an extract phase fromthe refined charging stock can be employed for the purposes of thisinvention.

The process of this invention can be better appreciated by the followingnon-limiting examples.

EXAMPLE 1 A middle distillate charge stock having an ASTM boiling rangeof 316 to 502 F. and a Saybolt color of +11 is charged to an extractorat the rate of 5,030 milliliters per hour. The middle distillate chargestock is contacted countercurrently with a furfural at a rate of 7500milliliters per hour. The temperatures of the extractor are F. bottomand 180 F. top temperature. The rafiinate phase is separated from theextract phase and a sample withdrawn and stripped of any dissolvedsolvent. The middle distillate after water washing of the furfuralsolsvent form the middle distillate has a Saybolt color of EXAMPLE 2 Thesolvent-contained raffinate phase from Example 1 is cooled to 81 F. andcharged into a liquid-liquid separator. A secondary raftinate is formedand removed from the extract phase. After water Washing the furfuralsolvent from the middle distillate fuel, the middle distillate fuel hasa Saybolt color of +9.

Examples 1 and 2 clearly demonstrate that a middle distillate fuel canbe obtained which has good color by maintaining the average temperatureat the time of separation of the secondary raflinate and secondaryextract phase within the temperature range of from about 60 F. to about130 F. Thus, the oil obtained after contacting the middle distillatecharge stock with furfural at a temperature of 180 F. had a Sayboltcolor of 5, whereas the charge stock had a Saybolt color of +11. Ofparticular importance is the color of middle distillate fuel that isobtained when the primary rafiinate is cooled to 81 F. Moreparticularly, the recovered fuel obtained utilizing the process of thisinvention has a Saybolt color of +9. The data set forth in the precedingexample clearly demonstrates the outstanding performance of the processof this invention for producing middle distillate fuels having improvedcolor and burning qualities utilizing a furfural solvent extractionprocess.

While this invention has been described with respect to various specificexamples and embodiments it is to be understood that the invention isnot limited thereto and that it can be variously practiced within thescope of the following claims.

I claim:

1. A solvent extraction process which comprises contacting a middledistillate charge stock with a furfural solvent in an amount sufficientto form a primary extract phase and a primary ratfinate phase,maintaining a raifinate outlet temperature above about 150 F.,separating the primary raflinate phase from the primary extract phase,reducing the temperature of the primary rafiinate phase to below about135 F. to form a secondary extract and secondary raffinate phase,separating the secondary rafiinate phase from the secondary extractphase while maintaining the temperature of the secondary extract phaseand the secondary rafiinate phase during separation below about 135 F.and recovering a middle distillate fuel from the secondary raflinatephase, provided that the furfural solvent during the formation of theprimary ratiinate phase and the primary extract phase contains colorimpurities which would produce a middle distillate fuel from the primaryraflinate phase which is darker in color than the charge stock.

2. A process of claim 1 wherein the furfural solvent comprises about 90%furfural.

3. A process of claim 2 wherein the furfural solvent comprisessubstantially furfural.

4. A process of claim 1 wherein the primary rafiinate is reduced intemperature to within the range of from about F. to about 130 F.

5. A process of claim 3 wherein the primary raffinate is reduced intemperature to within the range of from about 80 F. to about 130 F.

6. A process of claim 1 wherein the primary raffinate is reduced intemperature to within the range of from about F. to about F.

7. A process of claim 3 wherein the primary raffinate is reduced intemperature to within the range of from about 90 F. to about 110 F.

8. A process of claim 1 wherein the middle distillate fuel is kerosene.

9. A process of claim 3 wherein the middle distillate fuel is kerosene.

10. A process of claim 5 wherein the middle distillate fuel is kerosene.

11. A process of claim 7 wherein the middle distillate fuel is kerosene.

References Cited UNITED STATES PATENTS 2,121,323 6/1938 Manley et al208-327 3,205,167 9/ 1965 Demeester 208-327 3,247,101 4/1966 Woodle208327 3,291,727 12/1966 Woodle et a1 208327 HERBERT LEVINE, PrimaryExaminer US. Cl. X.R.

